#8326: Place heap checks common in case alternatives before the case -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: jstolarek Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: | Blocked By: None/Unknown | Related Tickets: #1498 Test Case: | Blocking: 8317 | Differential Revisions: Phab:D343 | -------------------------------------+------------------------------------- Comment (by simonpj): I'm sure this is do-able by knot-tying, but it'll need a bit of care. * Each alternative can start by emitting a pure blob of code that is a function of the GC plan * The GC plan is computed from the heap-allocation info from all the alternatives (this is the knot-tied bit) * So it must be possible to run the alternative `FCode` blobs without yet knowing the GC plan. * Currently `cgAlts` is strict in the plan, but I don't think it needs to be. After all, the code we generate for the alternatives does not depend on whether there's a heap check at the beginning. You probably need to allocate a label regardless since that is a monadic operation. So not trivial, but ought to be quite possible. ''Semantically'' the data dependencies are just fine! Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8326#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler